stone for roof conservation
they find a quarry somewhere more suitable, like an industrial estate in
the Midlands? This suggestion was made by an objector to a proposal
to re-open a quarry which had supplied the raw materials for hundreds of
historic buildings in the south west and for which no other source was
available. These sentiments are regularly expressed whenever a quarry
is proposed, regardless of its size, purpose or intended duration.
Clearly the notion that any similar stone will do instead is not one that
accords with those who are trying to conserve historic buildings.
it so important to use the correct stone? Building owners and
English Heritage have a duty to maintain and repair their buildings using
appropriate materials and techniques. Guiding principles advocate
the use of like for like repairs using authentic materials. But the
justification for doing this is not just philosophical. Technical
and aesthetic reasons can be even more important. Selecting a stone
which is to be pieced in or used to replace others in an old wall cannot
be done by a visual inspection alone . The old wall will have
weathered over time and its appearance will have changed, noticeably from
the effects of organic growth, especially lichen. The stone itself
will have been affected by the way that the other stones and mortars around
it have performed over time and its exposure to the elements.
|It is of course, highly likely that
stone for replacement or repair coming from the original source will perform
the best. Although initial appearance will be different it will weather
the same way and should start to match the host stones. Indeed the
type of lichens and other plants attracted are partly determined by the
minerals in the stone, so a reasonable match can be expected. The
minerals and pore structures of the new stone also need to be compatible
with those of the surrounding stones. A recent report  from Scotland
showed the harm that can arise where alternative stones are selected which
appear similar but are in fact, not compatible.
|Over the years, English Heritage
has been directly involved in searching for and sourcing appropriate stone
for many buildings. In some cases the original sources are no longer
available, or have not been worked for decades. Two recent examples
were carried out during the Roofs of England campaign which sought to try
to rejuvenate stone slating in England.
|Small-scale quarrying: Pitchford
Church The nave roof of Pitchford Church 
Shrewsbury needed to be re-roofed. Harnage stone-slates had not been
produced commercially for over a century. Old geological maps and
other records located previous and potential sources which were investigated.
Park Wood quarry was selected, not just because it was the original source
of stone for the Church roof, but because the physical characteristics
of the stone were eminently suitable. Most importantly, there was
a willing land-owner and although the site was a listed parkland, there
was a great deal of encouragement and help given by Shropshire CC mineral
planners. The delving took six weeks and although it was carried
out in the wettest month in Shropshire since 1841 sufficient stone was
won to recover the nave of the Church and also supply three other listed
buildings in the area. At its height the quarry presented quite a
scar on the landscape but four months later it was fully restored.
Planning permission has been renewed in case Harnage stone is needed again.
The Pichford delve during operation
The same area six months later
Pictures Chris Wood
|Dore Abbey 70,000 new
stone slates were needed to repair the roofs of Dore Abbey in Herefordshire.
There was a great deal of local enthusiasm for sourcing the stone locally
because it could provide farmers with an alternative income following the
ravages of foot and mouth disease. Again, a very helpful mineral
planning authority eased the difficulties of obtaining consents for these
small, temporary delves. Significantly, the Herefordshire Mineral
Planners pre-empted public objections by consenting 1/10 hectare areas
but once the quarry proved to be well managed quickly extended the consent
in time and area, when the initial stone was worked out. Old red sandstone
slates are now available again for repairing these distinctive roofs throughout
Herefordshire and the Welsh Marches.
|Difficulties sourcing supplies
two cases were relatively rare examples where new delves have opened and
successfully supplied material. It is becoming ever more difficult
to do this for a number of reasons. Some former quarries have been
worked out or built upon or the land is used for another purpose.
But the biggest constraint comes from objections from local residents or
special interest groups (such as ramblers, nature conservation bodies etc)
or from other environmental designations. Many former workings make
excellent nature reserves and are now designated as SSSIs or County Wildlife
sites. European designations cover other sites and to date, virtually
all proposals to win material Ė even on a temporary basis have been resisted.
SSSIs which are designated because of their geological interest, though
may be permitted because the new workings could expose new faces and other
material of interest.
|The Roofs of England campaign was
based on research carried out in the South Pennines  including the Peak
District National Park where there are particular problems. But even
outside the Park, in areas where there are no environmental designations
it can be extremely difficult to obtain consent. Re-opening a former
quarry at Moorhays Farm, near Chesterfield for a modest amount of stone
slates has taken five years to obtain consent because of concerted objections
from residents in the area.
|If new supplies are not forthcoming,
then the vacuum is filled by re-using slates from other buildings which
either means cannibalising farm buildings (often significant features in
the landscape) or theft which is becoming alarmingly common. The
alternatives are to use man-made concrete substitutes or importing stone
from India & the Far East. Whilst the latter may well provide
natural products, none of them have been tested and as yet, we have no
indication as to how they will perform in the English climate. It is of
course, hardly sustainable to transport stone half way around the world
whilst local sources are denied for environmental reasons.
|Opening quarries for small amounts
of building or roofing stone can be a difficult process. Both
quarrying and dressing are still essentially hand-crafted operations and
with relatively small outputs, profit margins are small. But where
there is a willing operator/entrepreneur and most importantly, supportive
land owner and planning authority and decent supply of material; then much-needed
stone can be obtained.
|Land owners often have potential
sources of material which have been used in the past to repair and maintain
their own buildings. More will be needed. To assess where the
priority lies for roofing will require a condition review of a sample of
their stone roofs followed by an assessment of which particular stones
are needed for repair and which are in short supply. Hopefully, the
original quarries lie on their own land, and can still provide good fissile
material. If there are good reserves, they could supply stone for
other roofs in the locality as has happened at Dore Abbey for example.
This would be a major boon to local conservation efforts, as well as potentially
providing income for the land owner. English Heritage would be happy
to share its experience of opening small quarries and processing the finished
|Chris Wood English Heritage
| A Technical Advice Note, Selecting
and Sourcing Stone for the Repair of Historic Buildings. English Heritage
Customer Services, PO Box 569, Swindon SN2 2YR Tel 0870 333 1181
Fax 01793 414 926 .
 The Performance of Replacement
Sandstone in The New Town of Edinburgh. Research Report TCRE,
Historic Scotland 2004. Edinburgh
 This is written up in detail
in English Heritage Research Transactions
Vol 9: Stone Roofing.pp 128-156. English Heritage 2003.
James & James, London
 Written up in English
Heritage Research Transactions Vol 9: Stone Roofing pp 1-34.
English Heritage 2003. James & James, London